BAGHDAD — Framers of Iraq’s new constitution said yesterday that they need more time to finish the document, a move that threatens the political momentum on which Washington has staked its strategy for drawing down forces from the country next year.

President Jalal Talabani, however, insisted that the parliament meet its Aug. 15 deadline to approve the draft charter. A showdown was expected today, the last day under the interim constitution for the committee to seek an extension.

Defense Secretary Donald H. Rumsfeld flew to Baghdad on Wednesday to insist that the Iraqis finish the constitution on time. But substantial differences remain among the Sunni Arab, Shi’ite and Kurdish factions despite weeks of intense deliberations.

Underscoring the stakes, the U.S. military announced yesterday that five American service members died in a pair of explosions in Baghdad the previous day. Their deaths brought the number of Americans killed in the past week to 16.

Members of the drafting committee had been warning for weeks that although 90 percent of the document was completed, the 71 members could not agree on a few key issues, including federalism, the role of Islam, distribution of national wealth and the name of the country.

With no sign of compromise, committee Chairman Humam Hammoudi said on his way into a meeting that he would recommend the group ask for a 30-day extension. After the meeting, one of the framers, Bahaa al-Araji, said the recommendation had been accepted.

Mr. al-Araji said Kurdish delegates wanted a six-month delay — the maximum amount under the interim constitution — but that Shi’ites and Sunni Arabs would accept no more than 30 days.

As word of a possible extension spread, however, U.S. officials began pressuring the Iraqis to stand by the timetable, Iraqi officials said.

The charter will be submitted to a referendum two months after ratification by parliament. If voters approve it, a new election will be held in mid-December, and the United States and its coalition partners can begin withdrawing forces by next summer.

Mr. Talabani, a Kurd, met yesterday with U.S. Ambassador Zalmay Khalilzad and then issued a statement underscoring “the necessity to finish the writing of the constitution at the scheduled time.”

Mr. Talabani demanded that “maximum efforts be exerted” to reach an agreement on the draft as scheduled. Iraqi officials, speaking on the condition of anonymity, said intensive consultations were under way last night to find a way out of the impasse.

Yet suspicions were running deep among the three factions. The Shi’ites were pressing for language declaring Islam the main source of legislation, whereas the Kurds wanted religious teachings to be one of several sources.

The Kurds were holding out for federalism, which many Sunnis fear will lead to the breakup of the state. Even among those who support federalism, broad differences exist on such details as the limits of regional power and a formula for distributing oil wealth.